Manufacturers of electric cartridge heaters have long had the problem of producing heaters of various diameters to fit within complementary bores of a size specified by a user, and this caused the manufacturer to stock a large amount of heaters in each diameter. On the other hand, the user of the heater frequently found that the part to be heated had been designed so that its bores were larger than the diameter of the heater on hand, or that the bores had been improperly drilled to a larger diameter, and this caused delay in use of the apparatus until proper diameter heaters could be obtained.
Cartridge heaters are frequently used to heat dies formed of steel, aluminum or other metal. If the metal sheath of the heater is in close engagement with the bore wall surface, the interengaging parts sometimes are fused or welded together in the event the cartridge heater fails, and this makes it difficult to remove the heater without affecting the dies. By use of my invention, this is overcome since the cartridge sheath would tend to weld to the sleeve, rather than to the bore surface, and the assembly may be removed from the bore without affecting the dies.
A further advantage of my invention is that it provides a method of conversion from the present measurement system to the metric system by sizing sleeves to suit. Generally, the invention effects a cost savings and means of standardization by a conversion kit method.
My invention eliminates the problems and accomplishes the advantages noted above by utilizing metal sleeve means in combination with a cartridge heater, the sleeve means having an inside diameter to closely receive the sheath of a cartridge heater, and having an outside diameter to closely fit within the larger diameter bore. The sleeve means is preferably made up of a plurality of sleeves of identical length, each sleeve being shorter than the full length of a heater, except a heater of minimum length, so that a plurality of sleeves may be used, in number to cover the various lengths to which the heaters are made.